Discovery and Biology of Spathius verustus Chao (Hymenoptera: Braconidae), a Potential Biological Agent on Two Monochamus Vectors of the Pinewood Nematode

Round 1

Reviewer 1 Report

The authors initiate efforts to find biological control agents for Monochamus alterenatus and M. saltuarius, vectors of the pine wilt nematode which causes pine wilt disease. Pine wilt disease is serious in Korea and elsewhere in Asia, and new control options are needed. This paper presents foundational work that is meant to set the stage for a future biological control program. The work is interesting but further revision of the manuscript is needed before the paper is acceptable for publication.

The authors provide a good review of the significance of pine wilt disease in Korea and the desire for a sustainable biological control program is clear. However, the authors fail to mention that both Monochamus species are native to Korea. This detail is critical. A fundamental premise of classical biological control is that the pest species has become problematic because it has escaped the effects of natural enemies, and the intent is to reunite the pest with those enemies. A classical biological control program in Korea for pine wilt nematode, native to North America, would be appropriate. However the premise for classical biological control does not hold for these Monochamus species. It may still be appropriate to look for natural enemies, but the broader purpose would be quite different, perhaps as part of conservation biological control , a very different strategy. (Thus, general comparisons of the current project to biological control efforts for other forest pests like Anoplophora glabripennis and Agrilus planipennis do not seem entirely relevant.)

The authors do not provide a review of previous surveys for parasitoids of Monochamus species in Korea.  In particular, the authors do not refer to the previously published work of Kim et al. 2016 and 2017 (Both appearing in the Proceedings of the Korean Society of Applied Entomology Conference; http://db/koreascholar.com/article.aspx?code-318043 and  http://db.koreascholar.com/article.aspx?code=334414). It is perhaps worthwhile to note that the second proceedings article also reports the discovery of Cyanopterus flavator, not mentioned in the current paper. I only have access to the abstracts of the papers, but the authors should clarify how the current study is different from those earlier efforts.

The field and laboratory methods are reasonable. The descriptions of the statistical methods are not clear. The authors simply need to specify which statistical test(s) was/were applied to which question and why.

The results are confusing. Numerous statements are made, perhaps reflecting numerical trends in the data, that are not supported by the statistical analysis.  For example, the authors state in lines 272-273 that “… the number of S. versutus increased with host size on M. alternatus (n=12, r=0.35, df=10, t=1.16, p=0.27)”. To their credit, the authors provide the statistics to show that the relationship is not supported statistically. But, the text creates confusion.  A more accurate description of the result would be, “We were unable to identify an effect of host size on the number of S. versutus on M. alternatus.” Throughout the results, the authors should avoid statements that are not supported by the accompanying statistics. It is unnecessary to repeat statistics in the text and in a table. One or the other will suffice. The authors appear to report proportions that are described as percentages (e.g., Y-axis of Figures 5 and 6). Table 4 seems unnecessary.

The discussion primarily seems to recap the results from the study. The authors do not offer much explanation about why these parasitoids, already present on the landscape, have not provided effective control of either host species.

In general, I found the paper to be longer than necessary.  The overall length could be reduced by at least 25%. Additional comments are available in the attached file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment. Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper makes an interesting and valuable contribution to the biological control of Monochamus vectors as PWN vector. The authors do a good job and in my opinion this manuscript meets the standard criteria required by Forests. However, I have a few comments and questions, listed below.

Line 34: delete ”tree“.

Line 35: Please unify the writing style of Latin names.

Line 67-69, Line 95-97: Lack of references support.

Line 95-104: Lines 95-97 say that a lot of research has been done in the United States, China and Russia. Why do lines 98-104 only list the research cases in the United States?If there is any relevant research, please add it.

2.3 Field survey: It is suggested that the author can do more heights of sentinel logs test.

Line 200-202: Can Figure 2C and 2D in the article be changed more clearly? I can't see the position of the male in Fig. 2C, or the author can circle it out.

Line 384: Please write the full Latin name at the beginning of the sentence.

Author Response

Please see the attachment. Thank you. 

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,

Thank you for the interesting manuscript and the improvement made.

However there are still some details that require second revision:

Lines 39-40 – Although some laboratory assays performed in the last century indicated the probability of some weevils (Curculionidae) or jewel beetles (Buprestidae) worldwide the insect-vectors of the pinewood nematode are wood-boring beetles from the genus Monochamus. So, the sentence should be:

The pinewood nematode spreads among its hosts by using wood-boring beetles such as long-horned beetles from the genus Monochamus as vectors [12,13, new 14].

 (new) 14. Sousa, E.; Bravo, M.A.; Pires, J.; Naves, P.; Penas, A.C.; Bonifácio, L.; Mota, M.M. Bursaphelenchus xylophilus (Nematoda; Aphelenchoididae) associated with Monochamus galloprovincialis (Coleoptera; Cerambycidae) in Portugal. Nematology, 2001, 3(1): 89-91.

Insert after Line 86 - A relatively high diversity of parasitoids were also found associated with M. galloprovincialis, the pinewood nematode insect-vector in Portugal, but are mainly idiobiont ectoparasitoids and generalists attacking a vast array of other insects living in dead and dying trees (new 37).

(new) 37. Petersen-Silva, R.; Pujade-Villar, J.; Naves, P.; Sousa, E.; Belokobylskij, S.  Parasitoids of Monochamus galloprovincialis (Coleoptera, Cerambycidae), vector of the pine wood nematode, with identification key for the Palaearctic region. Zookeys, 2012, 251: 29-48.

Empty line should be inserted in 115, to separate Materials and Methods title

Line 122 – Korean red pine (insert scientific name of the pine here, since is the first time it is cited)

Line 213 – Remove “according to”

Line 260 – From table 1 the study obtained 12 M. alternatus larvae parasitized and 25 parasitoid specimens (table 2). These numbers are too small for a consistent ANOVA statistical analysis and a small sentence should be added in line 260. However the counting the number of parasitized host larvae in Figure 4 is 39. Please confirm the data in Table 1.

Line 278-279 – Apparently the graph in figure 4 is only of M. alternatus (line 259). If so, this should be added in the figure’s legend.

Lines 290-291 – This sentence should be removed since is already and correctly inserted in the discussion (lines 322-323).

Line 321 – remove “they were”.

Line 323 - Sentence should be changed to: “This may indicate that S. verustus responds to ovipositional cues as S. agrilis, in in previous study (56).”  Since no study was made to identify the cues and the compared species is not a Cerambycid, the authors must reduce speculation to the minimum.

Lines 328 – “1) The parasitoids females were not attracted by kairomones from naked host…”

The study did not attempted to isolate any chemical compounds that were eventually released by the Monochamus larvae and could act as kairomones to the parasitoids. And according to Wang et al. there are no such kairomones emitted by A. planipennis larvae, the parasitoids was attracted by the tree volatiles released is response to the pest damage. Likewise, Gonçalves et al. 2020 also described the pine tree volatiles change dramatically in response to the Monochamus galloprovincialis feeding, which could be used as cues for the Pinewood nematode to exit the insect-vector body. Gonçalves et al. 2021 refer that M. galloprovincialis larvae and pupae hardly release any volatiles, therefore no chemical cue is expected to be available for the parasitoids when naked larvae were exposed.

So, the sentence should be changed: “1) The parasitoids females were not attracted to naked hosts since no chemical cues are expected to be released and act as kairomone”

Lines 388-389 – Gonçalves et al 2020 and Gonçalves et al 2021 could be refered as the ongoing research to break the pinewood nematode transmission from the infected wood to the insect-vector and later from the insect-vector to the healthy host pine tree, during feeding.   

Line 332 – “As no oviposition cue of S. verustus was identified.

Line 414 – replace “flight time” by “flight period”.

Attached zip with suggested new references related to the introduction and discussion. The comparison model is a Buprestid and the proposed references are recent research on the European Monochamus pinewood vector.

Comments for author File: Comments.rar

Author Response

Thank you very much for kind and useful comments. Please see the attachment. 

Author Response File: Author Response.docx